Biodegradable polymer materials are widely applied to medical materials, drug delivery systems, environmentally compatible materials, etc. In recent years, new functions besides these are further demanded and various researches have been conducted. Particularly, introducing a chemically modifiable functional group into a molecule of polyhydroxyalkanoate represented by polylactic acid is examined, and there are some reports about a compound to which a carboxyl group, a vinyl group or the like is introduced. For example, polymalic acid is known as a polyhydroxyalkanoate having a carboxyl group in the side chain. Among the polymers of this polymalic acid, there have been known α-type compounds represented by the chemical formula (14):
and β-type compounds represented by the chemical formula (15):
which are different in the way of polymer formation. Among these, as for the β-type polymalic acid and its copolymer, a polymer obtained by ring-opening polymerization of benzyl ester of β-malolactone represented by the chemical formula (16):
(R16: benzyl group) is disclosed in the specification of U.S. Pat. No. 4,265,247. In addition, as for the α-type polymalic acid-glycolic acid copolymer and other copolymers containing hydroxyalkanoic acid including glycolic acid, polymers obtained by copolymerizing a 6-membered cyclic diester monomer represented by the chemical formula (17):
wherein R17 represents a lower alkyl group such as a methyl group, an ethyl group, n-propyl group, an isopropyl group, and a t-butyl group and a benzyl group, etc., and a glycolide and lactide which are cyclic diesters, a lactone which is an ester by intramolecular ring closure reaction of ω-hydroxycarboxylic acid are disclosed in Japanese Patent Application Laid-Open No. H2-3415.
In addition, with regard to a polyhydroxyalkanoate having a carboxyl group on a side chain, it is disclosed in Macromolecules 2000, 33 (13), 4619-4627 that ring-opening polymerization of 7-oxo-4-oxepane carboxylate ester is conducted to prepare a polymer having an ester group on a side chain, which is further subjected to hydrocracking to prepare a polymer having carboxylic acid on a side chain. Biomacromolecules 2000, 1, 275 discloses a polymer to which benzyloxycarbonyl group is introduced at the α-position methylene group of a carbonyl group in the poly(ε-caprolactone) main chain by reacting poly(ε-caprolactone) with lithium diisopropylamide and further reacting with benzyl chloroformate. Macromolecular Bioscience 2004, 4, 232 discloses a polymer to which (benzyloxycarbonyl)methyl group is introduced at the α-position methylene group of a carbonyl group in the polylactic acid main chain by reacting polylactic acid with lithium diisopropyl amide and further reacting with benzyl bromoacetate.
With regard to a polyhydroxyalkanoate having a vinyl group on a side chain, Polymeric Materials Science & Engineering 2002, 87, 254 discloses a polymer obtained by ring-opening polymerization of α-allyl (δ-valerolactone). With regard to a polyhydroxyalkanoate having a vinyl group on a side chain, Polymer Preprints 2002, 43 (2), 727 also discloses a polymer obtained by ring-opening polymerization of 3,6-diallyl-1,4-dioxane-2,5-dione which is a 6-membered ring diester monomer.
As mentioned above, there have been reported polymers having new functions imparted by further introducing a functionality providing structure to a polyhydroxyalkanoate to which a chemically modifiable functional group has been introduced. In International Journal of Biological Macromolecules 25 (1999) 265, ring-opening polymerization of a cyclic dimer of α-malic acid and glycolic acid gives a copolymer of α-type malic acid and glycolic acid, and a polyester having a carboxyl group on a side chain is obtained by deprotecting the obtained polymer. It is described that carboxyl group of a side chain of this compound was subjected to chemical modification with a tripeptide, the obtained polymer was evaluated about cellular adhesiveness and good results were obtained.